<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      var num = +prompt("请输入一个数字");
      var sum = num;
      var last = num;
      for (var i = 10; i <= 10000; i *= 10) {
        // last = sum + num;
        // last  =
        // last = num
        last = num * i + last;
        sum += last;
        // console.log(sum);
      }
      console.log(sum);
    </script>
  </body>
</html>
